JOURNAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



OCTOBER, 1916. 



TEANSACTIONS OF THE SOCIETY. 



XIA^. — Originative Factors in Evolution. 

 By Pkofessoe J. Arthur Thomson, M.A. LL.D. 



Bead March 15, 1916. 



§ 1. A GOOD many years ago there was born in an apparently normal 

 Xorth of Scotland family a child who grew up to be a wise and 

 well-proportioned dwarf. He married and had children — -a certain 

 number of whom were dwarfs. The peculiarity re-appeared in 

 grandchildren and great-grandchildren, and one of the fourth 

 generation is now at the head of a successful business — a wise and 

 well-proportioned dwarf. The question before us, discussible if not 

 answerable, is. What conditioned the dwarf? This is one of the 

 fundamental problems in Biology — the origin of the distinctively 

 new. WTiether it be a clever dwarf, a mathematical genius, a 

 10-foot tailed cock, a copper-beech, a greater celandine with 

 laciniate leaves, the general problem is the same, the old problem 

 of new departures. Wltat are the originative factors in organic 

 evolutio7i '? 



§ 2. A problem so difficult demands cautious handling, and an 

 elementary introduction requires no apology. The first question 

 is as to the nature of the novelties that actually occur, and the 

 sound procedure is to take stock of all observed peculiarities or 

 differences marking off individual organisms of the same kind. 

 These " observed differences " must be measured and registered 

 without theory or prejudice. We compare the colour of the trout 

 we catch from different streams, the various numerical relations 

 of radial canals and sense-organs in a thousand jellyfishes, the 



Oct. 18th, 1916 2 H 



